An integration-type high-speed analog-to-digital converter

An analog-to-digital (A/D) converter consisting of a switched-capacitor integrator, comparator, and control circuit is presented. The conversion process consists of voltage-to-frequency (V/F) conversion to determine the upper M bits of an N-bit representation of an analog input voltage and the subsequent voltage-to-time (V/T) conversion to determine the remaining lower N -M bits. The total clock cycle required for N-bit resolution is 2^M+2^N-M at most. The circuits for the V/F and V/T conversion share most of the components and thus the converter can be implemented with the minimum component count. Error analysis shows that a conversion accuracy higher than 12 bits can be expected from its CMOS monolithic realization. Prototype converters built using discrete components have confirmed the principles of operation     

A flash Josephson A/D converter constructed with one-junctionSQUIDs

A novel approach to the construction of a flash-type Josephson A/D (analog/digital) converter is presented. Simulations show that one-junction SQUID (superconducting quantum interference device) comparators can have a greater than fivefold advantage in bandwidth over the two- or three-junction SQUIDs in an A/D circuit. Assuming a Nb junction technology, the simulations show that a 6-bit A/D converter using one-junction SQUID comparators could have a sampling rate of ~20 GHz with ~5 bits of resolution for a 5-GHz input signal. Detailed analysis and simulations of an A/D converter constructed with one-junction SQUIDs are presented. Further improvement can be made by using a coding algorithm which requires 2N-1 comparators, instead of N, for an N-bit A/D converter     

A microstep controller of a DC servomotor

A microstep controller of a DC servomotor is developed for accurate positioning and smooth movement at low-speed rotation. It consists of digital and analog positioning loops. Dividing one period of quadrature sinusoidal signals generated by an incremental encoder attached to a motor shaft into quarter sections, the digital loop controls the movement between the sections. The analog loop divides each section further into N equiangle segments to control the movement within each section. The effective angle resolution is thus 90°/MN with M being the number of slits etched on an incremental encoder. A prototype controller assembled using monolithic and hybrid integrated components has confirmed the principles of operation. Positioning accuracy was 0.009°±0.002°. A further improvement is possible with this controller by increasing the number of slits on the encoder and reducing the interpolation step size. Positioning accuracy is dominated ultimately by the amplitude fluctuation of quadrature sinusoidal outputs, and thus an automatic amplitude control should be incorporated into the encoder. The controller was first intended for applications such as crystal-pulling apparatus, astronomical observation systems, and tracking radars, which require smoothly rotating mechanisms, but it can also be applied to fine-positioning mechanisms in scanning electron and tunneling microscopes and semiconductor manufacturing equipment     

Analog-to-analog conversion with high normal mode rejection ratiofor power-line-frequency noise

A simple method that ensures high normal mode rejection ratio (NMRR) for power-line-frequency noise in dual-slope integration and voltage-to-frequency (V-F)-based A/D converters is proposed. Experimental results for normal mode rejection ratios above 90 dB achieved in an instrument designed with implementation of this method are also reported     

Magnetic anisotropy of perpendicular media on grooved structuresubstrate

Magnetic anisotropies were investigated for CoCr perpendicular magnetic films on grooved structure substrates (pitch length 2.1 μm) prepared by CF₄-reactive-ion etching. Perpendicular magnetic anisotropy decreases in the region where groove depth GD >650 A. The reduction is due to the inclination of the crystal growth axis on the groove surface. In-plane magnetic anisotropy, K_u∥, strongly depends on GD and saturation magnetization M_s. In a region of large GD and large M_s, Ku_∥ is mainly due to shape anisotropy. In a region of small GD and small M_s , K_u∥ is caused by perpendicular magnetic anisotropy, in addition to shape and magnetorestrictive anisotropy     

Measuring harmonic distortion and noise floor of an A/D converterusing spectral averaging

The author proposes to use spectral averaging techniques to measure the harmonic distortion and noise floor of an analog/digital (A/D) digitizing subsystem. The noise floor of an ideal B-bit A/D converter is derived in closed form. It is shown that this noise floor is a function of the A/D resolution B, the record length N, and the equivalent noise bandwidth E_B of the window function used in the discrete-Fourier-transform (DFT) computation. For an example, the noise floor is given for the case in which the magnitude square of the spectrum is averaged. Both experimental and simulation results are presented and it is shown that they are in good agreement with the theoretical results     

High-speed A/D conversion incorporating a QMF bank

A structure for analog-to-digital (A/D) conversion capable of attaining high speed and using an array of lower-speed A/D converters is introduced. The structure is based on a quadrature mirror filter (QMF) bank, except that the analysis filter bank is a switched-capacitor circuit, whereas the synthesis filter bank is normally a digital circuit. It is shown that the effect of mismatches among the A/D converters in the array is considerably reduced by the QMF bank. Simulation and experimental results verifying the good performance of the proposed approach are included     

High coercivity in melt-spun SmFe10(Ti,M)2 ribbons (M=V/Cr/Mn/Mo)

Magnetic properties of SmFe₁₀(Ti,M)₂ melt-spun ribbons were studied, where M is V, Cr, Mn, and Mo. The ribbons (M=V/Cr/Mo) quenched at 20 m/s exhibit the high coercivities of 4.2-5.5 kOe. Annealing the ribbons quenched at 40 m/s enhances their coercivities in the range of 5.9-10.0 kOe. In particular, SmFe₁₀ (TiV) and SmFe₁₀(TiCr) ribbons yield coercivities of 10.0 kOe and 7.9 kOe, respectively. This is the highest value among the reported melt-spun ThMn₁₂-type structure ribbons. The importance of Sm atmosphere during annealing in minimizing the Sm evaporation from ribbons is also demonstrated     

Automatic technique for measuring the Polder resonance in ferritespheres

An automatic technique for measuring the parameters of Polder resonance in polycrystalline ferrite spheres is proposed. The diagonal elements of the external susceptibility tensor versus DC magnetic field are calculated from the changes in resonance frequency and unloaded Q factor of a microwave cavity by perturbation theory. From these diagonal elements, all the elements of the intrinsic permeability tensor can be obtained. By fitting the theoretical curves to experimental data, the parameters of Polder resonance, ΔH M_s, and the g factor, are simultaneously calculated. The whole measurement procedure is controlled by a desktop computer. An accuracy of 5% is obtained in ΔH and M _s, and of 0.1% in the g factor     

Development of high-quality ceramic powders for Sr0.9Ca0.1Zn2-W type hexagonal ferrite for permanentmagnet devices

Fine ceramic powders of Sr_0.9Ca_0.1Zn₂ Fe₁₆O₂₇ (Sr_0.9Ca_0.1Zn ₂-W) ferrite, of almost single domain grain size ~1 μm, have been synthesized successfully by sintering for a few hours a mixture of SrCO₃, CaCO₃, ZnO, and α-Fe₂ O₃ in stoichiometric amounts at an effectively low temperature (T_s) of ~1100°C. Carbon dioxide evolves in the reaction Sr(Ca)CO₃+2ZnO+8 α-Fe₂D₃ &lrarr2;Sr(Ca)Zn₂Fe₁₆O₂+C₂ , making fine pores in the sample, which prevent large grain growth of the material and result in a very loose powder. The small ⩽10% substitution of Sr by Ca activates the reaction, but preserves the crystallization of the small-sized grains. This yields magnetic properties useful for most permanent magnet applications, with a promisingly high coercivity H_c~3650 Oe and saturation magnetization M_s~65 emu/g. A considerably better saturation magnetization M_s~85 emu/g can be obtained by sintering the samples at higher T_s~1300°C, but that results in a rather very low coercivity H_c~105 Oe     

Determination of overwrite specification in thin-film head/disksystems

A self-consistent write analysis using the Preisach model is presented and used to calculate overwrite in thin-film head/disk systems. Two overwrite characterization procedures are discussed, and for each of the procedures the calculated values are compared with measurements. Through a correlation of overwrite, nonlinear peak shifts, and readback output voltage the authors determine the overwrite requirement. They show that whereas -30 dB of overwrite will ensure a satisfactory overall performance of the recording system, a much lower overwrite, say -20 dB, can work in certain situations. An analytical implementation of the self-consistent model is presented and verified with measurements. The analytical approach can be used to determine the overwrite at any applied field for any head/disk combination. The authors introduce a normalized effective field h_n, which depends on M_rδ, H_c, and other head/disk parameters. It is shown that a value of h _n greater than 0.8 is needed for overwrite values of better than 25 dB. The importance of various head/disk parameters in optimizing the overwrite is also discussed     

Analysis of the noise sources in an optically pumped cesium beamresonator

The main noise sources that affect the clock signal detection in an optically pumped cesium beam resonator are determined and their influence on the clock S/N ratio is evaluated. The following noise sources are taken into account: atomic shot noise, fluorescence photon noise, laser frequency noise, and clock signal detection noise. A theoretical model that predicts the variations of the S/N ratio as a function of different parameters characterizing the atom-laser interaction is developed. The main conclusion concerns the saturation of S/N value for high atomic flux due to laser frequency fluctuations. All the theoretical predictions were experimentally verified     

High density magneto-optical recording using 0.67 μm band highpower laser diode

High-density optical recording on a magnetooptical disk has been achieved by a compact optical head that uses a 0.67-μm-band high-power visible-light laser diode. The recording density has been improved to 1.5 times that for conventional optical recording, using a 0.83-μm laser diode, as a result of the increase in linear density and track density. The C/N ratio for the readout signal is greater than 50 dB     

A variable hysteresis aperturing method for superconductingcounting A/D conversion

The authors present an aperturing method for superconducting counting A/D (analog/digital) converters. The scheme, called TRAP (time release after aperturing of pulses), utilizes a large β_L two-junction SQUID (superconducting quantum interference device) quantizer and plays on the ability to control the amount of hysteresis available in such a SQUID. Incoming information from the analog signal can be either immediately processed by the quantizer or trapped and outputted at a later time. The author explains how this control can be used to form a picosecond aperture for counting A/D converters, eliminating pulse-skipping problems. SPICE simulations confirm the ideal behaviour of the TRAP     

Lateral magnetic inhomogeneities in Co-Cr layers detected by FMR

Co-Cr layers deposited on Ge underlayers were investigated with ferromagnetic resonance (FMR). The thickness of the Co-Cr layers and the substrate temperature (T_s) during deposition were varied. Measurements with a vibrating sample magnetometer showed that an increase of T_s results in an increase of both the bulk saturation magnetization M_s and the perpendicular coercivity H_c^⊥. The FMR spectra, obtained with the applied field perpendicular to the sample, showed two resonances for all layers. The effective anisotropy field is positive for both resonances. The difference in effective anisotropy field does not change with thickness of the layer, but increases with increasing T_s. From this it is clear that the two resonances are not due to magnetic inhomogeneities in the growth direction, but must be due to lateral magnetic inhomogeneities. Inhomogeneities in composition, resulting in different values of M _s, or in geometric structure, resulting in different values of the demagnetizing factor N_d, are the most probable causes of the observed effects     

Magnetic properties of GdBa2Cu3O7crystals in high magnetic field

The magnetic properties of single crystals of GdBa₂Cu ₃O₇ were investigated in a magnetic field of up to 20 T applied parallel to the c axis in the 1.7-300 K temperature range. In the superconducting state, the field and temperature dependences of the critical current densities were deduced from the hysteresis of the half-cycle using Bean's critical state model. The Gd³⁺ paramagnetic moment was then studied. Above about 20 K, the M(H) isotherms were found to be given, at different temperatures, by the Brillouin function of the free Gd³⁺ ion. Below 20 K, the average magnetization does not obey the Brillouin law. The normal-state susceptibility was described by the free-ion Curie-Weiss law     

RF-DC differences of coaxial thermal standards

The RF-DC differences (δ) of thermal converters are calculated from complex transmission line theory. The Boella effect and the skin effect are considered. The formula δ=Af^1/2 +Bf² can be obtained by experiments and proved by comparison of converters. The uncertainty of δ is 0.01% at 1 MHz and 0.1% at 30 MHz     

Digital signal processing techniques for high accuracy ultrasonicrange measurements

Several digital signal processing (DSP) methods are analyzed and compared with respect to the expected errors for an ultrasonic range measurement arrangement. These include L1, L2 norms and correlation with different approaches for envelope extraction. The influence of different factors such as signal-to-noise ratio (SNR), sampling frequency, and digitizing resolution on measurement errors is analyzed using a synthetic approach through nearly 40000 simulations. Results show different performance levels involving accuracy, computing time, and cost for the studied methods, although all of them allow reduction of errors by several orders of magnitude     

Coupled magnetoelastic theory of magnetic and magnetostrictivehysteresis

It is demonstrated that hysteresis in the magnetostriction k is coupled to hysteresis in the magnetization M because of the dependence of the magnetostriction on the magnetization. At the same time, when stress is present, the magnetization is in turn coupled to the behavior of the part of the magnetostriction associated with domain moment rotation. An expression for the magnetostriction is formulated, and numerical modeling results for magnetostriction hysteresis are compared to experimental results. Although some features of the magnetostriction in iron and steel still need additional explanation, the main features of the magnetostriction are accounted for. These include liftoff (failure of the magnetostriction to return to its value in the demagnetized state as the hysteresis loop is cycled) and a magnetostriction increase after flux density B reaches its maximum and starts to decrease. A macromagnetic, multidomain formulation that yields zero magnetostriction in the demagnetized specimen is used     

CMOS Monolithic Metal–Oxide Gas Sensor Microsystems

This paper presents two mixed-signal monolithic gas sensor microsystems fabricated in standard 0.8-$muhbox m$CMOS technology combined with post-CMOS micromachining to form the microhotplates. The on-chip microhotplates provide very high temperatures (between 200$^circ$C and 400$^circ$C), which are necessary for the normal operation of metal–oxide sensing layers. The first microsystem has a single-ended architecture comprising a microhotplate (diameter of 300$muhbox m$) and a digital proportional-integral-derivative (PID) microhotplate temperature controller. The second microsystem has a fully-differential architecture comprising an array of three microhotplates (diameter of 100$muhbox m$) and three digital PID microhotplate temperature controllers (one controller per microhotplate). The on-chip digital PID temperature controllers can accurately adjust the microhotplate temperatures up to 400$^circ$C with a resolution of 2$^circ$C. Further, both microsystems feature on-chip logarithmic converters for the readout of the metal–oxide resistors (which cover a measurement range between 1$hbox kOmega$and 10$hbox MOmega$), 10-bit A/D converters, anti-aliasing filters, 10-bit D/A converters,$I ^2 C$serial interfaces, and bulk-chip temperature sensors. Carbon monoxide (CO) concentrations in the sub-parts-per-million (ppm) range are detectable, and a resolution of 0.2 ppm CO has been achieved.